Clinical features of multiple myeloma include bone resorption, which often leads to pathologic fractures and chronic pain. Free light chains are small enough to be excreted in the urine, where they can be detected and are called Bence-Jones proteins. Unlike normal plasma cells where the production of light chains and heavy chains are tightly balanced, neoplastic plasma cells often synthesize an excess of either light or heavy chains. Commonly the high level of M proteins causes red cells on peripheral blood smears to stack on one another in linear arrays like poker chips, a finding referred to as rouleaux formation. The most common monoclonal Ig is IgG in 55% of patients followed by IgA in 25% of cases. Polyclonal IgG appears as a broad band as opposed to a sharp protein bar in monoclonal Ig. A monoclonal Ig identified in blood is referred to as an M component that can be detected via serum protein electrophoresis. Multiple myelomas are B cell proliferations with neoplastic plasma cells that secrete a monoclonal Ig or Ig fragment as opposed to polyclonal Igs seen in an immune response.
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